1. Field of the Invention
The invention relates to human body temperature management systems and in particular to devices for therapeutically heating.
2. Description of the Prior Art
The human body is constantly producing heat when metabolizing food. This heat is an import part of bodily function and sometimes the human body can not produce enough heat and fall subject to hypothermia. Core body temperature is maintained near a constant level through biologic homeostasis. But when the body is exposed to cold its internal mechanisms may be unable to replenish the heat that is being lost to the environment.
U.S. Pat. No. 2,590,212 to Samuels (1952) is a flexible therapeutic heating pad device for heating a body part. It uses electric resistance heating coils to produce heat. The coils are embedded in a flexible pad that is worn or pressed against the body part to be heated. This device requires a large amount of electrical power to operate limiting its portability while in use.
U.S. Pat. No. 3,894,213 to Agarwala (1975) is a heating pad using a fluid, an electrically heated reservoir, a circulating pump and a fluid filled pad with an inlet and an outlet for the fluid to flow. The fluid is heated in the reservoir then pumped in to the inlet of the pad. There it circulates through the pad warming the person and then exits the pad via the outlet and returns to the reservoir. This device requires electrical power to heat the fluid and to pump the fluid through the pad.
U.S. Pat. No. 5,562,604 to Yablon (1996) is a portable therapeutic device for treating a patient undergoing hot or cold therapy. This device is comprised of a flexible containment bag means comprising a sealed closed-loop fluid channel containing a liquid, an electromagnetic pumping means, a self-contained source of a therapeutic temperature and microprocessor temperature control. While this device is configured for heating the liquid is heated in the temperature control unit. The heated liquid is pumped to the flexible containment bag using an electromagnetic pump. The flexible containment bag is warn against the person receiving the therapy. Heat is transferred from the bag which contains the liquid to the person. The liquid cools off and is returned to the self-contained source of therapeutic temperature control. This portable therapeutic device relies on an electromagnetic pump to move the liquid. Electromagnetic pumps require that the liquid it pumps be a good electrical conductor and uses electrical power to produce the magnet field to pump the liquid.
U.S. Pat. No. 4,077,390 to Stanley et al (1978) a heating pad is made by enclosing a supersaturated aqueous sodium acetate solution with an activator strip in a flexible container. The heating pad is charged by applying heat to the pad until the sodium acetate is completely dissolved in the water. As the pad is cooled the sodium acetate remains dissolved in the water forming the supercooled solution. When the user wants to release the latent heat trapped in the solution he activates the flexible metal strip which causes the solution to crystallize. Heat is released until the crystallization process finishes.
All of the aforementioned devices have the ability to heat a person. Each one has it's own method of accomplishing basically the same thing. Likewise each method has strengths and limitations. The Samuels device uses electrical resistance heating coils to produce heat. This method uses large amounts of electrical power making it infeasible for portable heating. The Agarwala device electrically heats a liquid and uses an electrically powered pump to move the heated liquid through a bladder. This method requires a large amount of electrical power and added weight of a pump both of which limit the portability of the device. The Stanley et al device is very portable for a one time use. However the amount of heat it produces is very limited and recharging the device takes a lot of time and requires a much larger device like a stove. None of these inventions use a form of combustion to produce heat. Typically combustion produces an intensely high temperature heat that will burn the skin of a person if they come in contact with it. This is unfortunate because a small amount of fuel like propane can produce a large amount of heat for a long period of time. However this intensely high temperature heat can be spread over a larger area to produce a safe and comfortable amount of heat for a person.